Under the Stars

Ever since I got my first camera I have wanted to shoot the night sky and notably the milky way. This desire awakened in me after seeing many amazing images which in various ways portrayed the part of the milky way which stands out from the rest of the MW – the density of stars, gasses etc are much higher along this “band”. I believed I had to travel to the southern parts of Europe in order to shoot the milky way. Great was my joy when I one late August evening soon two years ago discovered it right over my head.

A setting moon casts a golden glow across a very still lake. This is a pano from four horizontals. I panned my camera upwards in order to capture as much of the sky as possible.

Where I live approx 60 km north of Oslo, Norway, the MW is very visible from around the middle of August until early winter. In August around 11 pm it is positioned along the south/north axis before it slowly turns westwards. I always shoot the MW towards the south or west as it is most distinct in those directions.

Our days are not exactly 24 hours – they are actually 4 mins short of being 24 hours. In other words, if the MW is seen towards the south around eleven in the evening in the end of August it will be seen towards the south 60 days x 4 mins = 240 mins (4 hours) earlier two months later.

I always carry the following equipment when doing night photography: Headlamp plus spare batteries and a regular torch, a cloth to wipe off damp from the lens if necessary, tripod, spare camera battery, camera and a fast wide angle lens. What is a fast lens? Lenses that are designed to offer apertures of f2.8 or lower are usually considered fast lenses or fast apertures. If you would like to learn more about aperture make a Google search and you’ll find plenty of resources.

Since full frame cameras or medium format cameras have larger sensor surfaces than crop cameras they will collect more light and hence yield a better result. A crop camera or aps-c camera will also produce more noise with less details at the same iso settings as a full frame camera. However, none of this should deter anyone with a crop camera from going out and enjoy the magic. And with the rapid advances in sensor technology we have seen the past years these differences between sensor sizes are not so pronounced as they used to be. You can read more about FF vs crop here.

A composite image – the waterfall and the MW are shot at different times and then blended in Photoshop.

But, how on earth do I compose my images when it is utterly dark? First of all, I drive to locations with very little or no light pollution so that the MW stands out clearly in the night sky. With some practice it is easy to locate. Next I push up the iso to max and shoot exposures at only a few secs to nail the comp. When I am happy with my composition I set the camera to around 25/30 secs. Longer exposure times than this will produce star trailing since the earth and the stars move relatively to each other. And I shoot with my lens wide open. For my lenses it means f2.8. In daylight I have tested where infinity is on my lenses so that I know where to set the focus ring. Auto focusing in the dark is not an option. The lens or camera (Pentax) has to be set to manual focusing. The next step is setting the iso. I try various iso settings until I have something that gives me a relatively even histogram. It is vital for me to check the histogram after each shot.

A decent straight out of camera histogram:

But what if it is impossible to achieve a relatively even histogram? The histogram shows no clipping of the highlights but on the left side there is huge bump which starts as a straight line – no nice curving at all at that end. If you know your way around photoshop and know how to blend exposures you shoot one extra exposure for the shadows at for instance two minutes. If you want even more shadow detail you can for example set the aperture to f4 and reduce the iso and perhaps shoot a four minute long exposure for the shadows.

Trying to overly push the shadows in post when having shot at a high iso usually never yields a good result (see my end notes). There are magenta color casts all over the place and excessive noise. I am not very fond of images where the shadows only are a black ocean of nothingness, in other words, silhouettes. So for me it is vital to produce night images which offer a decent level of shadow detail. The Pentax K-1 comes with a timer in Bulb mode so making long exposures is a breeze. With my former cameras I always had to keep track of the time myself and that was an added stress factor for one who now and then is plagued with fear of the dark.

In my beginning days of shooting the MW I found that shooting it wasn’t particularly difficult. The tricky part was finding out how to edit these night shots. I spent numerous hours in front of the computer trying to find ways to make the MW stand out, to give it pop, contrast and so on. All my efforts have resulted in this tutorial.

Image straight out of camera:

The finished image:

The image is from the middle of Sept 2015 and the MW had turned quite a bit towards west.

Stellarium is a free program which can be downloaded to your desktop, and it shows the whereabouts of the MW at any given day and time of the day.

Turning on and off the headlamp all the time doesn’t exactly help our night vision so knowing where all the vital buttons on the camera are is a relatively good idea. And if you are shooting with others the light must be turned off save times when no one is shooting. Ruining others’ images because we haven’t done our homework isn’t very nice, to put it like that.

I have arrived at that shooting a pano of the MW this far north is a tad pointless. Firstly, one third of the MW is hidden from view. However, that part is visible for those living further south on this globe. Secondly, up here the MW is very “high” in the sky whereas for the southerners it is hanging much lower, something which of course simplifies things in regards to shooting panos. When that is said, it is of course possible to make panos like this:

End of sept 2016. Five 15mm verticals handblended in Photoshop. We had some aurora that evening as seen to the far right (north).

Shooting at a high iso is detrimental to the image quality. Both luminance and color noise are introduced liberally to our dear efforts at night photography. Lightroom offers a good raw noise reduction algorithm. The problem is that noise reduction softens the image and details become blurred so it is always a balancing act between noise and detail when we edit our night images.

There are of course a few workarounds. We can shoot our shadow exposure before it becomes too dark at a narrower aperture and much lower iso. Then we wait until it is sufficiently dark to shoot our sky exposure. But, if the luminosity values are too wide between the two exposures the blending can turn out to be a very painful affair. What I mean is that the shadow exposure will have highlights that are way too bright and we face fringing and weird artifacts along our blending lines. In other words, not a bad idea to have a third exposure that bridges the gap.

Shooting verticals can be a great way of capturing a larger portion of the MW:

A second method of increasing the quality is using star tracking devices. They make it possible for the camera to follow the motion of the stars so that we can shoot much longer exposures than 25 secs for the sky and hence reduce the iso considerably. As mentioned in my Astro Tracer blog post the camera sensor is linear whereas a wide angle lens creates a curvature so that we may get star trailing in the corners (when shooting wide angle). The Pentax K-1 is equipped with an in-camera star tracker which enables the sensor to follow the motion of the stars.

The greatest enemies of night photography are clouds and the moon. Even a half moon washes out the milky way so that it becomes more or less impossible to shoot. So keep an eye on the moon phases.

I have of yet not tried focus stacking in the dark since that is a pretty time consuming affair. Instead I make sure that my tripod is fully extended so that I can achieve infinite focus (hyperfocal distance) from around 2,5/3 meters (distance from my camera/lens) when shooting f2.8 and 15mm. An object around 3 meters from my camera should then be in focus. There are several hyperfocal distance apps that can be downloaded to our cell phones. I haven’t tried any of these.

I always shoot auto white balance at night and adjust the WB in post. When it is iso 1600-3200 dark the sky is very blue and beautiful in my raw files, but as it becomes increasingly darker colors become washed out and the raws often get this yellow tint. To put it like this; things aren’t exactly static when doing night photography and that is one of the reasons why I prefer auto white balance.

Some end notes:

Some claim they getter a better result if they expose to the right. In other words, they boost the iso so that the histogram is pushed to the right. More light to the sensor they claim yields a cleaner image. Then we have this thing called iso variance. A camera with great iso variance can achieve better results at a lower iso setting than what the histogram suggests we should use. This means that we increase the exposure in post but yet achieve a very good end result.

For example if I get a balanced histogram at iso 6400 I opt to shoot iso 1600 and then push the exposure two stops in post. If the camera has good iso variance I will in many ways achieve a better result than shooting iso 6400. Notice that doubling the iso is the equivalent of one stop of light. Since a camera’s dynamic range suffers dramatically at high iso levels we will also achieve a better dynamic range at lower iso settings, and we preserve our highlights. Anyway, we have to experience on our own to find what works best with the gear we have.

From dpreview: “The K-1 is as close to being ISO Invariant as we’ve seen, meaning there’s no cost to shooting at ISO 100 and pushing the files later, rather than using a higher ISO. This means you can keep the ISO down and protect multiple stops worth of highlight information that would otherwise be pushed to clipping by the hardware amplification.”

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